JEP 186: Collection Literals

OwnerBrian Goetz
Created2013/06/20 20:00
Updated2014/07/10 20:47
Componentspecification / language
Discussionlambda dash dev at openjdk dot java dot net


A collection literal is a syntactic expression form that evaluates to an aggregate type, such as an array, List, or Map. Many languages support collection literals. A List literal in Java might look like:

List<Integer> list = #[ 1, 2, 3 ];

Collection literals were proposed for Project Coin and naturally complement the library additions in Java SE 8. Collection literals can reduce boilerplate code, improve performance, and increase safety.


This is a research JEP. The sole goal of this JEP is to explore the design space sufficiently to be able to propose a feature JEP (or recommend that the feature not be pursued.)


It is not a goal of this research JEP to produce a production-ready implementation or specification.

Success Metrics

This research JEP will be judged successful if it produces a design that we wish to move forward to a feature JEP, or else certainty that we do not wish to proceed with this feature.


Collection literals can increase programmer productivity, code readability, and code safety.


Being able to initialize arrays, lists, sets, and maps with a compact expression offers many benefits, including:

While a minimal solution that works for arrays, Lists, and Maps would be "trivial", we would like to explore beyond such a simple-minded solution, leveraging target typing and which might enable an extensible set of types to exploit this feature.